Desulfurizing roast of pyrite bearing polymetallic raw material

ABSTRACT

A method comprises heating the material to be treated without access of air at a temperature of 700° to 800° C. for a period of 1-2 hours, and then subjecting this material to subsequent magnetic separation. 
     It is advisable that the furnace walls surrounding the material under treatment be heated to a temperature which is 100° C. to 200° C. higher than the boiling temperature of the volatile components of the material. Upon completion of the heating operation, the material being treated is cooled at a rate of 2 to 4 deg. per minute, whereafter iron sulphides are removed therefrom by means of magnetic separation, the intensity of magnetic field ranging from 1000 to 2000 oersted, and then copper sulphides are separated, with the field intensity ranging from 4500 to 6000 oersted.

BACKGROUND ART

The present invention relates to metallurgy, and more particularly, to amethod of treating pyrite bearing polymetallic material to obtainelemental sulphur, pyrrhotine concentrate to be subjected to furthertreatment with the purpose of removing the residual sulphur therefrom,and producing iron-ore pellets as well as the product enriched withnonferrous, rare and noble metals separated to form selectiveconditioned concentrates by any conventional technique.

This invention can find advantageous application in the treatment ofpyrite bearing polymetallic material which includes non-ferrous, rareand noble metals.

There is known in the art a method of treating pyrite concentrate, whichcomprises heating (roasting) this material in the atmosphere of inertgas without air access, and then subjecting it to flash roasting at atemperature within the range of 1800° C. to 2000° C. Here, the pyriteconcentrate, containing 46% by weight of iron and 52.8% by weight ofsulphur, is subjected to thermal decomposition with the resultantformation of matte and separation of elemental sulphur. The matte isthen granulated and roasted in a furance in a fluidized bed, this beingaccompanied by the liberation of sulphuric gases to be utilized for theproduction of sulphur acid. The resultant iron concentrate may containup to 67% by weight of iron.

However, the aforedescribed method fails to provide for the recovery ofnonferrous, rare and noble metals. It is only suitable for the treatmentof pyrite concentrate high in sulphur.

There is a known method for treating pyrite concentrates less rich insulphur and iron, containing 38.5% by weight of iron, 39.1% by weight ofsulphur and 20% by weight of gangue. This method comprises an oxidizingroasting of the initial material, carried out in a furance in afluidized bed at a temperature of 965° C. The resultant roast is thensubjected to a reducing magnetizing roasting at a temperature of 550° to650° C., followed by magnetic separation thereof. The oxidized roastundergoes magnetic separation at a magnetic field intensity of 100 to600 oersted. The resultant magnetic product undergoes pelletizing andfiring, whereafter it contains up to 66% by weight of iron, thus beingrendered suitable for blast-furnace smelting.

This method also fails to provide for the recovery of nonferrous, rareand noble metals.

Recovery of nonferrous and noble metals from pyrite concentrates iseffected by means of oxidizing roasting of initial material in afurnaces in a fluidized bed at a temperature of 900° C. The resultantgases are used for the production of sulphuric acid, and the oxidizedroast is granulated in 40% solution of calcium chloride to be thereaftersubjected to secondary roasting conducted at a temperature of 1250° C.in cylindrical rotary kilns. The resultant iron-containing product isemployed in blast furnaces. The gases evolved in the process ofsecondary roasting contain chlorides of nonferrous and noble metals.

The above-described method, however, includes two-stage roasting ofhigh-grade pyrite concentrates, effected at high temperatures, whichsubstantially increases the operating costs.

Another known method used for the recovery of nonferrous and noblemetals from polymetallic material comprises subjecting this material tooxidizing roasting, which is effected in a furnace in fluidized bed at atemperature of 704° to 816° C. until pyrrhotine is obtained. Thepyrrhotine is then subjected to aqueous lixiviation in an autoclave,with oxygen under pressure being fed therein. The nonferrous metals arepassing to a solution from which they are further precipitated by meansof hydrogen sulphide.

However, the roasting procedure combined with autoclave lixiviation andsubsequent hydrometallurgical recovery of nonferrous metals renders theabove method cumbersome and complicated.

Various techniques employed today in the treatment of rebelliouspolymetallic ores, notwithstanding numerous modifications andimprovements, fail to satisfy growing demands of nonferrous metallurgyin high-grade selective concentrates. Thus, the increase of total volumeof pyritous polymetallic concentrates, intermediary products and tailsmakes it absolutely necessary and essential to develop effective andcomprehensive methods of treating these types for materials to yieldvaluable products, such as elemental sulphur, iron-ore pellets andconcentrates of nonferrous metals.

DISCLOSURE OF THE INVENTION

It is therefore the primary object of the invention to provide a methodof treating pyritous polymetallic raw material, which will promote moreeffective recovery of iron, sulphur, as well as nonferrous, noble andrare metals, as compared to known methods used for similar purposes, andto simplify the flowsheet of treating pyritous polymetallic material,minimize the losses of valuable minerals and to reduce the operatingexpenses involved in the treatment of pyrite bearing polymetallicmaterial.

According to the invention, there is provided a method of treatingpyritous polymetallic material, comprising heating this material withoutair access and its subsequent separation into products by means ofmagnetic separation, wherein the heating is effected prior to magneticseparation at a temperature of 700° to 800° C. for a period of 1-2hours.

With the initial material being heated to a temperature on the order of700°-800° C. for a period of 1-2 hours, the valuable minerals and ganguecontained therein do not undergo any chemical conversion, and pyritedissociates in accordance with the following reaction:

    FeS.sub.2 →Fe.sub.n S.sub.n+1 +S°,

where n=from 5 to 10.

This makes it possible to obtain about 43-45% by weight of pyritesulphur in an elementary state and to have diamagnetic pyrite convertedinto ferromagnetic hexagonal pyrrhotite. The process of thermaltreatment (roasting) is accompanied by sulphidizing of the oxidizedminerals of nonferrous metals, decrepitation of the grains of mineralsand self-grinding of the material, which results in a higher yield ofvaluable metals, improved separation of minerals during magneticseparation and lower energy requirements for subsequent crushingoperations.

In heating the initial material to a temperature below 700° C., there isobserved incomplete transition of pyrite into ferromagnetic pyrrhotine,whereas at temperatures above 800° C. and with durations of heatingperiods exceeding 2 hours, there takes place transition of ferromagneticpyrrhotine into nonmagnetic pyrrhotine with a lower content of sulphur,down to troilite. This sharply reduces the recovery of iron found inmagnetic pyrrhotine concentrate.

It is advisable that the walls surrounding the material under treatmentbe heated to a temperature which is 100° to 200° C. higher than theboiling temperature of the material volatile components.

With this condition observed, a gap is formed between the furnace wallsand the material under treatment, which is filled with gaseous andvaporous products formed during roasting the operation. The presence ofgaseous and vaporous products makes for sliding movement of the treatedmaterial during its descent, reduces the extent of its fusion andeliminates its sticking to the furnace walls, thus ensuring successfultreatment of material of practically any degree of moisture and particlesize.

If the temperature of the furnace walls surrounding the material undertreatment is by 100° C. lower than the boiling temperature of thematerial's volatile components, the desirable results cannot beattained. An increase in the temperature of the furnace walls by morethan 200° C. is economically unprofitable.

Where copper-containing material undergoes treatment, its cooling ispreferably effected at a rate of 2 to 4 deg. per min, and magneticseparation is preferably carried out in two stages, initially separatingiron sulphides at a magnetic field intensity ranging from 1000 to 2000oersteds, followed by separation of copper sulphides to be effected atthe field intensity ranging from 4500 to 6000 oersted.

Effecting the cooling of the material being treated at a rate of 2 to 4deg. per min. makes possible the transition of the copper mineralscontained in the initial material, in particular, cubic diamagneticchalcopyrite into tetragonal modification with somewhat lower content ofsulphur possessing magnetic properties. The cooling of the roastedmaterial at a rate lower than 2 deg. per min prolongs the duration andincreases the cost of treatment of pyritous material, whereas a higherrate of cooling, above 4 deg. per min, brings down the recovery ofcopper, to copper concentrate.

By carrying out magnetic separation in two stages and within theaforeindicated range of the magnetic field intensity, it becomespossible to simplify the technological process of treating pyritouspolymetallic material and reduce operating costs, as compared to knownmethods which comprise multiple roasting of initial material or itstreatment in autoclaves. A decrease in the intensity of magnetic field,as compared to the recommended value in accordance with the invention,below 1000 oersteds in the first stage and below 4500 oersteds in thesecond stage, will respectively result in lower yields of pyrrhotine andcopper concentrates. An increase in the intensity of magnetic fieldabove 200 oersteds in the first stage and above 6000 oersteds in thesecond stage will impair the quality of pyrrhotine and copperconcentrates.

BEST MODE OF CARRYING OUT THE INVENTION

The invention will be further explained by the following illustrativeExamples.

EXAMPLE I

Ore refuse (tails) poor in pyrite, containing 28% by weight of iron,33.5% by weight of sulphur, 0.85% by weight of lead, 0.94% by weight ofzinc, 0.26% by weight of copper, 30% by weight of quartz, were subjectedto heating without air access at a temperature of 750° C. for a periodof 1 hour. The recovery of volatile matter was 15.6 wt.%. Theheat-treated material was cooled at a rate of 2 deg. per min, and thenwas subjected to magnetic separation in an aqueous medium with alaboratory magnetic analyzer, at a magnetic field intensity of 1000oersteds. The yield of the first magnetic fraction obtained, i.e.pyrrhotine concentrate, was 43.04 wt.%. The pyrrhotine concentratecontained 59.42 wt.% iron, 0.09 wt.% copper, 0.17 wt.% lead, 0.08 wt.%zinc and 5.0 wt.% quartz. The recovery from the initial material was91.34% iron, 14.90% copper, 8.61% lead, 3.66% zinc and 7.17% quartz. thenonmagnetic fraction was subjected to secondary magnetic separation inaqueous media at a magnetic field intensity of 4500 oersteds. Therecovery in the second magnetic fraction, i.e. magnetic concentrate, was2.25% by weight of the initial material. The resultant copperconcentrate contained 8.96 wt.% copper, 0.79 wt.% lead, 0.61 wt.% zinc,13.2 wt.% iron and 12.12 wt.% quartz. Recovery from the initial materialwas 77.58% copper, 2.09% lead, 1.46% zinc, 1.26% iron and 1.02% quartz.The end nonmagnetic fraction contained 70.43 wt.% quartz, 5.3 wt.% iron,0.05 wt.% copper, 1.94 wt.% lead, and 2.28 wt.% zinc. The recovery fromthe initial material into nonmagnetic fraction contained 91.80% quartz;7.40% iron; 7.53% copper; 89.24% lead and 9.4.84% zinc.

EXAMPLE 2

Pyrite concentrate, containing 38 wt.% iron, 43.3 wt.% sulphur 0.06 wt.%lead, 0.32 wt.% zinc and 12.0 wt.% quartz, was heated without air accessat a temperature of 800° C. for a period of 1 hour. The yield ofvolatile components was 18.76 wt.%. The heat-treated material was cooledand then separated in an aqueous medium at a magnetic field intensity of1500 oersteds. The recovery of the magnetic fraction was 80 wt.%. Themagnetic fraction contained 57.5 wt.% iron, 37.0 wt.% sulphur, 0.04 wt.%lead, 0.18 wt.% zinc, and 1.65 wt.% quartz. Recovery from the initialmaterial was 98.34% iron, 55.17% sulphur, 46.80% lead; 37.12% zinc, and8.91% quartz. The nonmagnetic fraction contained 7.0 wt.% iron, 5.0 wt.%sulphur, 2.0 wt.% lead, 1.25 wt.% zinc and 66.80 wt.% quartz. Recoveryfrom the initial material was 1.97% iron; 53.30% lead; 63.43% zinc,1.86% sulphur and 89.16% quartz.

EXAMPLE 3

A molybdenum industrial product having the following composition, inpercent by weight: 13.50 molybdenum, 34.26 iron, 44.80 sulphur, 5.65quartz, was subjected to heating without air access in a continuousshaft furance. The material under treatment descended by gravity. Thefurance walls were maintained at a temperature of 150° C. higher thanthe dissociation temperature of the pyrite contained in the molybdenumproduct in an amount of 65 percent by weight. It is possible either toraise or lower the temperature of the surface walls, either up to 200°C. or down to 100° C., respectively, depending on the content ofvolatile components in the initial material. The amount of pyritesulphur driven off the initial material was 42.72 wt%. Subsequentmagnetic separation effected at the intensity of magnetic field of 2000oersteds results in a magnetic fraction containing 58.92 wt.% iron,36.75 wt.% sulphur, 1.91 wt.% molybdenum, 0.73 wt.% quartz. The yield ofiron recovered from the initial material into the magnetic fraction was94.35%. The nonmagnetic fraction contained 45.34 wt.% molybdenum and18.45 wt.% quartz. The former and the latter were recovered from theinitial material in an amount of 95.68% and 94.70% respectively.Subsequent flotation of the nonmagnetic fraction resulted in ahigh-grade molybdenum concentrate containing 54.14 wt.% molybdenum and3.12 wt.% quartz.

EXAMPLE 4

Ore, containing 38.6 wt.% iron, 5.64 wt.% copper, 0.35 wt.% lead, 3.51wt.% zinc, 2 g/t gold, 100 g/t silver and 45.4 wt.% sulphur, wassubjected to heating without air access at a temperature of 700° C. fora period of 2 hours, followed by subsequent cooling effected at a rateof 4 deg. per min. Copper was present in the ore in the form ofdiamagnetic tetragonal chalcopyrite. The heat-treated product, afteriron sulphides has been removed therefrom by magnetic separation at theintensity of magnetic field of 1500 oersteds, was subjected to secondaryseparation with the magnetic field intensity being 6000 oersteds. Therecovery of copper to copper concentrate was 87.0%. The nonmagneticproduct contained lead, noble metals and zinc.

From the above it follows that the method of the invention can besuccessfully used in the treatment of various pyrite bearingpolymetallic materials for the recovery of elemental sulphur, pyrrhotineconcentrate, the latter being high-grade material used for theproduction of iron-ore pellets and sulphuric acid, selective copperconcentrate and the product rich in nonferrous, rare and noble metals,which is further separated to form selective conditioned concentrates.

The method of the invention makes it possible to carry out comprehensivetreatment of pyrite bearing polymetallic materials, minimizing the lossof valuable materials.

INDUSTRIAL APPLICABILITY

Laboratory investigations and industrial trials carried out to confirmthe expected results of the invention have been successful. Thecommercial product under treatment was pyritous molybdenum producthaving the following chemical composition: 31.99 wt.% molybdenum; 18.18wt.% iron, 42/25 wt.% sulphur; 4.42 wt.% quartz; and pyrite polymetallicore containing 40.0 wt.% iron, 46.7% sulphur, 0.22 wt.% zinc, 0.92 wt.%copper and 4.03 wt.% quartz.

Nonmagnetic concentrate resulting from the initial material contained,in the first instance, 98% molybdenum and 96% quartz whereas in thesecond instance it contained 80% zinc, 85% lead and 90% quartz. Thecopper concentrate resultant from the initial material contained 88%copper. Elemental sulphur recovered from the initial material amountedup to 45%. The resultant magnetic product contained 90-98% iron. Afteroxidizing roasting, the resulting iron concentrate contained 62-67% ironand 0.5% sulphur.

What we claim is:
 1. A method for treating a pyrite bearing polymetallicmaterial comprising ferrous, non-ferrous, rare and noble metals, whichcomprises: heating said material in a walled vessel without air accessat a temperature of about 700° to 800° C. for about 1 to 2 hours,wherein the walls of the vessel surrounding said polymetallic materialare heated to a temperature of about 100° to 200° C. higher than theboiling temperature of the volatile components of the polymetallicmaterial; and magnetically separating the products formed.
 2. The methodof claim 1 wherein the heated material is cooled at a rate of 2 to 4degrees per minute, thereby effecting a transition of copper sulfidescontained in the polymetallic material from cubic diamagneticchalcopyrite into its tetragonal modification, followed by a two stagemagnetic separation, wherein in the first stage iron sulfides areseparated at a magnetic field intensity of about 1000 to 2000 oersteds,and in the second stage copper sulfides are separated at a magneticfield intensity of about 4500 to 6000 oersteds.
 3. A method for treatinga pyrite bearing polymetallic material comprising ferrous, non-ferrous,rare and noble metals, which comprises: heating said material in awalled vessel without air access at a temperature of about 700° to 800°C. for about 1 to 2 hours; cooling the heated material at a rate of 2 to4 degrees per minute, thereby effecting a transition of copper sulfidescontained in the polymetallic material from cubic diamagneticchalcopyrite into its tetragonal modification, followed by a two stagemagnetic separation, wherein in the first stage iron sulfides areseparated at a magnetic field intensity of about 1000 to 2000 oersteds,and in the second stage copper sulfides are separated at a magneticfield intensity of about 4500 to 6000 oersteds.
 4. The method of claim3, wherein the walls of the vessel surrounding said polymetallicmaterial are heated to a temperature of about 100° to 200° C. higherthan the boiling temperature of the volatile components of thepolymetallic material.
 5. The method of any of claims 1 or 3, wherein atthe heating temperature of 700° to 800° C., the pyrite dissociates inaccordance with the equation:

    FeS.sub.2 →Fe.sub.n S.sub.n+1 +S°

where n=5 to 10.